The purpose of this study is to describe the epidemiology of pulmonary hypertension in individuals with HIV infection and to investigate its pathogenesis. We propose to conduct a prospective observational cohort study to determine the association between highly active antiretroviral therapy (HAART) and viral suppression in HIV-infected patients who have been identified to have pre-clinical pulmonary hypertension (Aim 1). In addition, we will investigate the mechanistic role of the HIV-1 Nef protein and HHV-8 infection in the development and progression of pulmonary hypertension in individuals with HIV (Aim 2). We will also investigate endothelial function in HIV-infected patients with pulmonary hypertension (Aim 3).